Method of and apparatus for purifying zinc metal



3 Sheets-Sheet l G HBY P. GINDER ET AL METHOD OF AND APPARATUS FOR PURIFYING ZINC METAL Filed April e, 1935 March 12, 1935.

March 12, 1935. GlNDER r AL 1,994,354

METHOD OF AND APPARATUS FOR PURIFYING ZINC METAL Filed April 6, 1953 5 Sheets-Sheet 2 35 J4 J0 zy 40 5? INVENTOR5 ATTORNEYS March 12, 19 P. M. GINDER ET AL METHOD OF AND APPARATUS FOR PURIFYING ZINC METAL Filed April 6, 1933 3 Sheets-Sheet 5 a R BY WH ATTORNEYS Patented Mar. 12, 1935 UNITED STATES METHOD OF AND APPARATUS FOR PURIFY- ING ZINC METAL Philip M. Ginder, Palmerton, Pa, and Harold G. Hixon, Depue, Ill., asslgnors to The Newlersey Zinc Company, New York, N. Y., a corporation of New Jersey Application April 6, 1933, Serial No. 664,736

8 Claims.

cadmium, or other metal impurities of higher and lower boiling points than zinc. The invention particularly contemplates the provision of certain improvements in removing lead and cadmium, or the like, from zinc metal by methods involving the action of a reflux column as described in the copending applications for Letters Patent of the United States of Leon S. Holstein and Philip M. Ginder, Serial No. 540,566, filed May 28, 1931 and a fractionation column as described in the co-pending application for Letters Patent of the United States of Philip M.

Ginder, Willis M. Peirce and Robert K. Waring,

Serial No. 620,634, filed July 2, 1932.

The present invention involves subjecting vapor derived from impure zinc metal contaminated with lead and cadmium to a reflux condensing treatment in which a vapor purified of lead is obtained and delivered to a fractionation treatment from which molten zinc metal purified of cadmium is obtained, and is particularly characterized by utilizing the same source of heat for volatilizing the impure zinc metal and for supplying heat to the fractionation treatment. Heat for both these purposes may thus for example be generated by a gas fired heating chamber surrounding the retort in which the impure zinc is volatilized, and may be conducted to the cadmium-eliminating column by conduction or by convection by means of exhaust gases from said gas fired heating chamber. The heat supplied to the fractionation treatment is appropriately controlled to effect the contemplated elimination of cadmium.

The apparatus of the invention comprises a plurality. of retorts for distilling zinc metal operatively mounted in the heating chamber or laboratory of an appropriate furnace structure. A reflux column for the elimination of lead, or the like, is operatively associated with each retort. The communicating means between a retort and its associated column permits the flow of metallic vapor from the retort to the lower end of the column and the countercurrent flow of refluxedmolten metal from the column to the retort. Each of these reflux columns has an outlet near its upper end communicating with a conduit for collecting metallic vapor. A fractionation column, particularly constructed for eliminating cadmium or the like, is thermally associated with the heating chamber of the furnace, so that heat in controlled amount may be supplied thereto. The aforementioned conduit is arranged to deliver metallic vapor and any condensed metal to the cadmium-eliminating fractionation column at a point intermediate its ends, and this column 5 is provided with means permitting the withdrawal of purified zinc metal from its base and of cadmium-rich vapor from its top.

The novel. features of the invention will be best understood from a consideration of the accom- 10 panying drawings, in which Fig. 1 is a sectional elevation of an apparatus embodying the invention taken on the section line 1--1 of Fig. 2,

Fig. 2 is a section of the apparatus taken on the section line 22 of Fig. l, and Fig. 3 is a front or side elevation of the apparatus.

The apparatus illustrated in the drawings comprises a furnace structure 10 having a central longitudinal partition 11 dividing the interior of the furnace into two adjacent and communicating heating chambers or laboratories 12. A horizontal row of zinc distillation retorts 13 is arranged in each heating chamber 12. The two horizontal rows of retorts are set back to back against the central wall 11 and are mounted at a slight inclination from the rear or back toward the front where they extend through appropriate openings in the two side or front walls of the furnace structure. The retorts 13 are made of suitable refractory material, such for example, as silicon carbide. A lower row of clay or other suitable refractory retorts 14 are mounted in the heating chambers 12 as deflectors for the heating gases flowing through these chambers. The retorts 14 are empty and serve merely to shield the redistilling retorts 13, placed directly above, from the direct impingement of the flames in the common heating chamber 12, in a conventional manner well understood in the art. The furnace construction, mounting of the retorts therein and the firing of the furnace with fuel gas in conjunction with a recuperator may advantageously follow in general the practice of the conventional Belgian spelter retort furnace.

The apparatus shown in the drawings has two operating units, one on each side of the central wall 11. These two units are identical and comprise three distillation retorts and associated leadeliminating reflux columns *arranged to deliver zinc vapor, purified with respect to lead, to a cadmium-eliminating fractionation column. Consideration will now be given to the construction and operation of one of these units, it being understood that the other unit (on the other side of the central wall 11) is constructed and operates in the same manner.

The cadmium-eliminating fractionation column is mounted in a compartment 15 built within the confines of the heating chamber 12 by two walls 16 of silicon carbide or other refractory material of good heat conductivity extending from the front wall of the furnace to its central wall 11. It will be understood that there is one compartment 15 on each side of the furnace, and that the two compartments are back to back, with two retorts 13 on one side of each compartment and one retort 13 on the other side thereof, as best illustrated in Fig. 2 of the drawings.

The cadmium-eliminating fractionation column consists of a stack of trays 1'7 of fire clay, silicon carbide or equivalent refractory material. The trays 17 are rectangular in form with side walls bevelled in such fashion that the trays can be stacked one above the other. The bottom of each tray has a transverse slot or opening 18 approximate one end thereof. The upper surface of the bottom of each tray is provided with transverse ribs 19 parallel to the slot 18; the ribs being of progressively increasing height'from the end nearest the slot to the end furthest from the slot. The trays 17 are stacked in staggered relationship so that the bottoms thereof form a column of superposed horizontal bafiles through which metallic vapor ascends and molten metal descends in zig-zag paths. The ribs 19 serve to retain shallow pools of molten metal on the bottom of the trays. The cascade effect of molten metal pouring over the ribs facilitates intimate contact between the ascending vapor and the descending molten metal. The top of the cadmium-eliminating fractionation column (17) extends through an opening in the arch or roof 20 of the furnace. A dephlegmator 21 having two or more staggered transverse baffles 22 is mounted on top of the column 17 and in communication therewith and is operatively connected to an appropriate condenser (not shown) forthe cadmium-rich vapor discharged from the top of the column. The tem-' perature of the dephlegmator 21 may be controlled, for example by placing a regulated amount of heat insulation material around the dephlegmator.

The outer end of each of the zinc distillation retorts 13 is connected by an elbow pipe 23 to the bottom of a lead-eliminating reflux column. Each reflux column comprises a cylinder 24, of fire clay or other appropriate refractory material, having an opening in the bottom thereof registering and communicating with the upper end of the elbow 23. The top of the cylinder 24 is closed by a plate 25 appropriately luted with mud or the like to prevent the escape of zinc vapor. The cylinder 24 is surrounded by appropriate heat insulating material 26 (such as refuse zinc oxide) confined in place by a steel jacket 2'7 supported in its operative position in front of the furnace in any appropriate manner.

The lead-eliminating reflux columns (24) are provided with spaced and superimposed bafiles 28 in the form of saucer plates. The saucer plates are circular with a segment cut away and are provided on their straight edges with an upwardly projecting rib whereby shallow pools of molten metal will be retained thereon. The saucer plates may be mounted within the cylinder 24 in any suitable manner (as for example by appropriately positioned depending pins) and are arranged with their cut-away segments staggered to provide a tortuous or zig-zag path for the countercurrently flowing vapor and molten metal.

One end of an elbow pipe 29 extends through the cover plate 25, and the other end of the elbow pipe communicates with a down-comer 30 mounted on and communicating with a closed trough or conduit 31. The conduit 31 extends along the entire side of the furnace and is mounted at a slight inclination from each end to a point opposite the cadmium-eliminating reflux column. The conduit 31 is supported by a sheet metal trough 32 lined internally with appropriate refractory material, such for example as tamped loam or clay 33. The trough 32, as well as the reflux columns 24, are supported by a suitable frame-work or brackets '34 secured to the buckstays of the furnace.

The downcomers 30 communicate with the conduit 31 through appropriate apertures in the top or cover of the conduit. Each aperture may be closed by means of a movable brick or damper 35 to prevent the escape of zinc vapor from the conduit when cleaning or changing retorts or reflux columns. The elbow pipe 29, the downcomer 30 and the conduit 31 may be made of fire-clay or other suitable refractory material.

Each retort 13 is provided with a charging well 36 communicating with the retort through an elbow pipe 37. Molten zinc metal to be purified is poured from a charging ladle 38 into a trough 39 discharging into the well 36.

The conduit 31 has at its lowermost point (opposite the cadmium-eliminating fractionation column) a lateral opening 40 communicating with a downcomer 41. An elbow pipe 42 connects the downcomer 41 with the cadmium-eliminating fractionation column at a point approximately half-way between its base and top. A pipe 43 conveys molten metal from the base of the cadmiumeliminating column to a crucible 44 or other appropriate receptacle for purified zinc metal.

In the operation of the apparatus shown in the drawings, the metallic vapor evolved from .the baths of boiling zinc metal in the retorts 13 passes through the elbows 23 into the associated reflux columns. The zinc vapor is purified with respect to lead by refluxing and/or rectification in the refiux or rectifying columns. The resulting purified zinc vapor passes out of the reflux columns through the elbow pipes 29, the downcomers 30 and theconduit 31 to the lateral opening 40 and downcomer 41 and thus into the cadmium-eliminating fractionation column. Any molten metal condensing in the conduit 31 flows by gravity to the lateral opening 40 and thence into the cadmiumeliminating fractionation column.

Heat is supplied to the cadmium-eliminating fractionation column through the walls 16, in regulated amount so as to rectify continuously the mixture of zinc and cadmium entering the column through the pipe 42. Thus, the ascending metal vapor becomes progressively enriched in cadmium while the descending molten metal is progressively free from cadmium, and cadmium-rich vapor flows out of the top of the column, through the dephlegmator 21, and refined zinc metal (that is, zinc metal with greatly decreased cadmium content) flows from the base of the column into the receptacle 44, from which the purified metal is ladled-out, or otherwise removed.

Molten zinc metal (of the grade to be refined) is charged from time to time (or continuously if desired) into each retort 13 (through the troughs 39 and wells 36) to maintain an appropriately uniform volume of molten metal in each retort.

Each retort is continuously operated until the lead content of the molten metal therein has increased to such a high percentage that the vapor delivered by its associated reflux column to the conduit 31 has as high a lead content as can be tolerated in the purified zinc metal. Such a retort is then cut out of operation, is cleaned of the lead-high metal therein, and is then recharged with molten zinc metal of the grade undergoing purification.

Heat for the cadmium-eliminating fractionation column is supplied, in the apparatus of the invention, by the same source that heats the zinc distillation retorts (namely, the gas-fired heating chamber 12), by conduction through the walls 16. When the apparatus is operating under normal conditions an appropriate amount of heat will be thus supplied to the cadmium-eliminating fractionation column to assure its proper functioning. In the apparatus illustrated in the drawings, the supply of heat to the cadmiumeliminating fractionation column can be regulated by either or both of the two following expedients: I

(1) The walls 16 are provided with shelf supports 45 so that a lining of heat-insulating brick can be built thereon, thereby lowering the supply of heat to the cadmium-eliminating column.

(2) Ports 46 are provided in the wall 16 for permitting hot gases from the heating chamber 12 to enter the compartment 15 and circulate around the cadmium-eliminating column. Such of these ports 46 as are not required to be kept open are closed by loose brick. The front wall of the compartment 15 is provided with. removable brick in order to permit convenient adjustments of these heat-regulating agencies when required.

While we have in the foregoing description of the invention particularly referred to the elimination of lead and cadmium from zinc, it will be understood that we have used those metal impurities (i. e. lead and cadmium) as representative of metal impurities of higher and lower boil-' ing points than zinc. Similarly in the appended claims, we have used the metal impurities lead and cadmium as representative of any metal impurities associated with the zinc metal having higher and lower boiling points, respectively, than zinc.

We claim:

1. The method of purifying zinc metal contaminated with lead and cadmium characterized in that metallic vapor derived from the impure zinc metal ascends a reflux column in contact with descending molten metal resulting from condensation of ascending vapor, and zinc vapor purified with respect to lead is conveyed from the top of the reflux column to a fractionation column in which ascending vapor becomes progressively enriched in cadmium and descending molten metal becomes progressively free of cadmium, and zinc metal purified of both lead and cadmium is removed from the base of said fractionation column, heat being supplied to the fractionation column in controlled amount from the same source of heat utilized for volatilizing the impure zinc metal.

2. An apparatus for purifying zinc metal containing lead and cadmium comprising a heating I chamber, a retort operatively mounted in said chamber, means for conveying metallic vapor from said retort to the base of a lead-eliminating reflux column, a cadmium-eliminating fractionation column thermally associated with said heating chamber, means'for conveying metallic vapor reaching the top of said lead-eliminating reflux column to said cadmium-eliminating fractionation column, and means permitting the withdrawal of purified zinc metal from the base and cadmium-rich vapor from the top of said cadmium-eliminating fractionation column.

3. An apparatus for purifying zinc metal containing lead and cadmium comprising a heating chamber, a plurality of retorts operatively mounted in said chamber, a lead-eliminating reflux column operatively associated with each retort, a cadmium-eliminating fractionation column thermally associated with said heating chamber, a common collecting system operatively associated with the upper ends of said leadeliminating reflux columns and adapted to deliver metallic vapor and any condensed metal to a point intermediate the ends of said cadmiumeliminating fractionation column, and means permitting the withdrawal of purified zinc metal from the base and cadmium-rich vapor from the top of said cadmium-eliminating fractionation column.

4. An apparatus for purifying zinc metal containing lead and cadmium comprising a plurality of retorts, a lead-eliminating reflux column operatively associated with each retort, a cadmiumeliminating fractionation column, a source of heat for said retorts, means for conveying heatfrom said source of heat to said cadmium-eliminating fractionation column, and means for conveying metallic vapor reaching the top of said lead-eliminating reflux columns to said cadmiumeliminating fractionation column.

5. An apparatus for purifying zinc metal containing lead and cadmium comprising a heating chamber, a plurality of retorts operatively mount-- ed in said chamber, a lead-eliminating reflux column operatively associated with each retort, means for conveying metallic vapor from said lead-eliminating reflux column to a common collecting system, a cadmium-eliminating fractionation column thermally associated with said heating chamber, and means for conveying metallic vapor and any condensed metal from said collecting system to said cadmium-eliminating fractionation column.

6. An apparatus for purifying zinc metal containing lead and cadmium comprising a heating chamber, a plurality of retorts operatively mounted in said chamber, a lead eliminating reflux column operatively associated with each retort, means permitting the flow of metallic vapor from each retort to the lower end of its associated reflux column and the countercurrent flow of molten metal from the reflux column to the retort, means permitting the flow of vapor from the top of each reflux column to a common conduit, and a cadmium-eliminating fractionation column thermally associated with said heating chamber and operatively connected to said conduit.

'7. An apparatus for purifying zinc metal containing lead and cadmium comprising a heating chamber, a retort operatively mounted in said chamber, a lead-eliminating reflux column operatively associated with said retort, a cadmium eliminating fractionation column mounted in a compartment built within the confines of said heating chamber and adapted to be heated thereby, and means for conveying metallic vapor reaching the top of said lead-eliminating reflux column to said cadmium-eliminating fractionation column.

8. The method of purifying zinc vapor contaminated with lead and cadmium in which zinc metal is volatilized and the resulting vapor subjected first to a reflux condensing treatment in 5 which a vapor purified of lead is obtained and then delivered to a i'ractionating treatment from which molten zinc metal purified of cadmium is obtained, characterized in that a common source of heat is utilized for volatilizing the impure zinc metal and for supplying heat to the iractionating treatment.

PHILIP M. GINDER. HAROLD G. HIXON. 

